Cover member for a gas combustion heads, and gas burner comprising such a cover member

ABSTRACT

A cover member for gas combustion heads. The cover member has at least one tubular base structure. And the tubular base structure is formed by knitting at least one metal wire.

The present invention relates to a metal cover member for premix burner gas combustion heads.

The present invention also relates to a gas or vapourized liquid fuel burner comprising such a cover member.

BACKGROUND OF THE INVENTION

As is known, in premix combustion heads, i.e. in which gas and air are mixed upstream from the combustion region where the flame is generated, the perforated metal combustion head from which the inflammable mixture is emitted can be covered with a specially constructed metal cover member.

Covering the combustion head with a metal cover member is particularly advantageous by enhancing heat exchange by radiation, while at the same time protecting the metal structure of the combustion head underneath. High modulation ratios and high-thermal-power premix applications can thus be achieved, which would otherwise be impossible on account of the severe thermal stress to which the combustion head is subjected.

The metal cover member also prevents the combustion head underneath from overheating to the extent that hazardous backfiring occurs.

Finally, the porosity of the metal cover member over the combustion head improves distribution of the fuel gas/air mixture, while at the same time reducing flame temperature and, hence, nitric oxide emissions.

In premix radiant burners, known solutions employ appropriately shaped woven or sintered cover members fitted to the combustion heads.

In the case of a burner with a cylindrical perforated combustion head, the woven or sintered cover member is folded to fit completely over the cylindrical surface of the combustion head, the free portions of the cover member are welded together, and the cover member so formed is welded to the combustion head.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cover member for gas burners, and a gas or vapourized liquid fuel burner comprising such a cover member, which is improved with respect to currently marketed types.

According to the present invention, there are provided a cover member for gas combustion heads, and a gas burner comprising such a cover member, as claimed in the accompanying independent Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Two non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows a layout of a premix gas burner featuring an innovative cover member;

FIG. 2 shows an enlarged detail of the perforated combustion head of the FIG. 1 burner fitted with the cover member which is the main object of the present invention;

FIG. 3 shows a number of stitches of a tubular base structure from which the cover member in FIGS. 1 and 2 is formed;

FIG. 4 shows a tubular base structure made using at least one drawn wire and knitted by means of a first knitting operation;

FIG. 5 shows a cover member formed by means of a second knitting operation using at least one tubular base structure formed by means of the first knitting operation; the tubular base structure is the one shown in FIGS. 3 and 4;

FIG. 6 shows an enlarged detail of the cover member in FIG. 5;

FIG. 7 shows a cover member formed by weaving a number of tubular base structures as shown in FIGS. 3 and 4;

FIG. 8 shows an enlarged detail of the cover member in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Number 10 in FIG. 1 indicates a premix gas burner featuring an innovative cover member in accordance with the present invention.

Burner 10 comprises a main body 11 supplied with fuel gas or vapourized liquid fuel by a pipe 12. Fuel gas flow along pipe 12 is controlled in the normal way by a pressure regulator 13 connected to main body 11 by a conduit 14.

Pipe 12 terminates with a nozzle 15 at the end projecting inside body 11.

A fan 16, integral with main body 11, provides for feeding into main body 11 the amount of primary air required to burn the gas, or vapourized liquid fuel, supplied by nozzle 15.

A substantially cylindrical, perforated metal combustion head 17 projects from body 11.

As shown in FIG. 1, combustion head 17 is fixed at a first end 17 a, as stated, to main body 11, and is closed at a second end 17 b by a cap 18.

As shown in FIGS. 1 and 2, the cylindrical outer surface 17 c of perforated metal combustion head 17 is covered with a cover member 19 b (FIGS. 7 and 8) in accordance with one embodiment of the present invention.

As shown particularly in FIG. 2, combustion head 17 has a number of openings 20 through which the fuel gas/air mixture flows from body 11 and combustion head 17 outwards to where the mixture is ignited to form the flame (not shown). As stated, the outer surface 17 c (FIGS. 1, 2) of combustion head 17 is fitted with cover member 19 b.

With reference to FIGS. 5 and 7, the cover member 19 a (FIG. 5), 19 b (FIG. 7) is formed by interlacing at least one tubular base structure 40 shown by way of example in FIG. 4.

FIG. 3 shows a number of stitches 31 a-31 g of a tubular base structure 40 (FIG. 4). Stitches 31 a-31 g are formed by knitting, by means of a first knitting operation, at least one metal wire 32 on a known knitting machine (not shown).

More specifically, as shown in FIG. 3, wire 32 is knitted using a knitting method commonly used, for example, in the manufacture of hosiery.

This method produces a tubular base structure 40, as shown in FIG. 4, in which stitches 31 a-31 g are looped using a method also commonly used in the knitting industry, and particularly in the manufacture of nylon stockings.

Advantageously, though not necessarily, the tubular base structure in FIG. 4 has a diameter of about 0.5 mm to 4 mm, and may be compressed to facilitate subsequent processing.

Advantageously, though not necessarily, wire 32 from which stitches 31 a-31 g are formed has a diameter of 0.05 mm to 1 mm.

Wire 32 is normally formed by drawing alloys resistant to high temperature and corrosion, such as NiCr or FeCrAl.

The tubular base structure 40 (FIG. 4) described is much lighter than stranded wire (not shown) used in conventional cover members (not shown). A stranded wire, in fact, is formed by combining a number of wires or fibres, and gives rise to a solid, heavy structure.

The tubular base structure 40 in FIG. 4, on the other hand, is characterized by being lightweight and extremely porous.

The porosity of cover member 19 a (FIG. 5), 19 b (FIG. 7) is a fundamental parameter in combustion applications.

Porosity, in fact, affects nitric oxide emission values, and reduces the load losses of combustion head 17; and adequate porosity of cover member 19 a, 19 b also aids in preventing backfiring.

The light weight of cover member 19 a, 19 b reduces thermal inertia, which is an important factor in reducing the heating time of the burner at start-up. In fact, the shorter the heating time is, the more stable the flame will be. Also, when the burner is turned off, faster cooling reduces thermal stress of combustion head 17, thus reducing wear. The light weight of cover member 19 a, 19 b also means less material is required.

The number of needles (not shown) used to produce tubular base structure 40 (FIG. 4) determines to some extent the elasticity and porosity of the finished article.

The same knitting method used to produce tubular base structure 40 may also be used to produce cover member 19 a in FIGS. 5, 6.

In actual fact, the cover member 19 a in FIG. 5, which represents a first embodiment of the present invention, is formed by means of a second knitting operation using at least one tubular base structure 40 formed using the first knitting operation described with reference to FIGS. 3 and 4.

Performing a second knitting operation using at least one tubular base structure 40 advantageously produces a tubular cover member 19 a as shown in FIG. 5, and which can be fitted directly onto the combustion head. In this case, no welding is required to loop cover member 19 a, thus simplifying manufacture and use of cover member 19 a.

In the second knitting operation, it is essential to control the overall elasticity of cover member 19 a and form a type of knit which, once fitted on, permits thermal expansion of combustion head 17 during operation of burner 10.

Once fitted on, cover member 19 a adheres to combustion head 17.

Though the solution proposed is particularly suitable for cylindrical combustion heads 17, this does not exclude the possibility of using cover member 19 a on combustion heads of other shapes or on flat structures.

When producing cover member 19 a, it is important to avoid ladders which, in service, are particularly hazardous by giving rise to backfiring. Ladders may be avoided by using special knit configurations known in literature.

The type of knit also determines the porosity of the final structure.

In a second embodiment of the present invention shown in FIGS. 7 and 8, as opposed to the second knitting operation described with reference to FIGS. 5 and 6, tubular base structures 40 in FIG. 4 can be assembled by straightforward weaving on a frame (not shown), and the finished article may be flat or tubular, depending on the type of loom used.

One example of a cover member 19 b of this type is shown in FIGS. 7 and 8. The FIG. 8 detail shows the weft 50 and warp 51 configuration typical of a cover member 19 b woven on a loom (not shown).

More specifically, the weft 50 is defined by a number of tubular base structures 40 a, 40 b, 40 c, and the warp 51 by tubular base structures 40 d, 40 e, 40 f; and weft 50 and warp 51 are woven on a frame (not shown).

Tubular base structures 40 a-40 f are all formed as described with reference to FIGS. 3 and 4.

The elasticity achieved by weaving as in FIGS. 7 and 8 is also ensured by the elasticity of tubular base structures 40 a-40 f.

Unlike cover member 19 a in the first embodiment, however, cover member 19 b in the second embodiment poses no danger of laddering.

Various types of weave can be used to obtain the desired porosity.

Both the intrinsic characteristics of combustion head 17 and knitting or weaving cover member 19 a or 19 b provide for achieving the porosity and elasticity of cover member 19 a, 19 b required when applied to premix burners 10.

More specifically, the porosity of cover member 19 a, 19 b provides for generating the flame front inside and downstream from cover member 19 a, 19 b (in the flow direction of the premixed mixture), thus averting any danger of backfiring.

The elasticity of cover member 19 a, 19 b enables it to be fitted on cold, and permits in-service thermal expansion of the supporting combustion head 17.

Another advantage, as stated, of the cover member 19 a, 19 b proposed is that it can be fitted onto perforated combustion head 17 and used with no need for welding to loop it, thus simplifying production and use of the cover member.

Moreover, once fitted on, cover member 19 a, 19 b generally adheres to perforated combustion head 17. In some applications, however, it may prove useful to weld it to combustion head 17.

Advantageously, though not necessarily, the single wire 32 (FIG. 3) used to form tubular base structure 40 may be made of high-temperature-resistant alloy, such as NiCr or FeCrAl. 

1) A cover member (19 a, 19 b) for gas or vapourized liquid fuel combustion heads (17); the cover member (19 a, 19 b) being characterized by comprising at least one tubular base structure (40), and each tubular base structure (40) being formed by means of a first knitting operating using at least one metal wire (32). 2) A cover member (19 a, 19 b) as claimed in claim 1, characterized in that said cover member (19 a) is formed by means of a second knitting operation using at least one tubular base structure (40) formed by means of said first knitting operation. 3) A cover member (19 a, 19 b) as claimed in claim 1, characterized in that said cover member (19 b) is formed by means of a weaving operation using at least one tubular base structure (40) formed by means of said first knitting operation. 4) A cover member (19 a, 19 b) as claimed in claim 1, characterized by being in the form of a seamless stocking. 5) A cover member (19 a, 19 b) as claimed in claim 1, characterized in that said tubular base structure (40) has a diameter of 0.5 mm to 4 mm. 6) A cover member (19 a, 19 b) as claimed in claim 5, characterized in that said tubular base structure (40) is formed using at least one wire (32) of 0.05 mm to 1 mm in diameter. 7) A cover member (19 a, 19 b) as claimed in claim 6, characterized in that said wire (32) is formed by drawing high-temperature-resistant materials, such as NiCr or FeCrAl alloys. 8) A premix gas or vapourized liquid fuel burner (10), characterized by comprising at least one cover member (19 a, 19 b) as claimed in claim
 1. 